Differential Diagnosis for Hard Nodules on Extremities and Trunk

Single Most Likely Diagnosis

• Scleroderma: This is a group of diseases that result in the hardening and tightening of skin and connective tissues. The presence of hard nodules on the extremities and trunk could be indicative of scleroderma, especially if accompanied by other symptoms such as skin thickening and limited mobility.

Other Likely Diagnoses

• Rheumatoid Arthritis (RA) with Rheumatoid Nodules: RA can cause the formation of firm nodules under the skin, often found on the elbows, hands, and feet. These nodules are a common extra-articular manifestation of RA.
• Gout: Gouty tophi, which are deposits of uric acid crystals, can form hard nodules under the skin, typically on the extremities. These are more common in patients with long-standing, untreated gout.
• Calcinosis Cutis: This condition involves the deposition of calcium in the skin, which can form hard nodules. It can be associated with various conditions, including autoimmune diseases and hyperparathyroidism.

Do Not Miss Diagnoses

• Malignancy (e.g., Metastatic Disease): Although less common, hard nodules on the skin can be a sign of metastatic cancer. For example, breast cancer or lung cancer can metastasize to the skin, forming hard nodules.
• Infectious Diseases (e.g., Mycobacterial Infections): Certain infections, such as leprosy or other mycobacterial infections, can cause skin nodules. These conditions are critical to identify due to their potential for serious morbidity if left untreated.

Rare Diagnoses

• Ehlers-Danlos Syndrome: Some types of Ehlers-Danlos syndrome can lead to the formation of subcutaneous nodules due to the abnormal structure of collagen.
• Sjögren's Syndrome: This autoimmune disorder can cause a variety of skin manifestations, including nodules, though this is less common.
• Multicentric Reticulohistiocytosis: A rare condition characterized by the formation of skin nodules and erosive arthritis, due to the proliferation of histiocytes.

Each of these diagnoses has distinct clinical features and associated conditions that can help guide the diagnostic process. A thorough medical history, physical examination, and appropriate diagnostic tests are essential for determining the underlying cause of hard nodules on the extremities and trunk.